Change iovec len from usize to u32

[MarcoROG]

Changes

Changing the type of iovec len from usize to u32

Resolves #4548

Reason

This is to better reflect the buffer size and prevent buffer overflows.

...

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check CONTRIBUTING.md.

PR Checklist

• [ ] If a specific issue led to this PR, this PR closes the issue.
• [ ] The description of changes is clear and encompassing.
• [ ] Any required documentation changes (code and docs) are included in this PR.
• [ ] API changes follow the Runbook for Firecracker API changes.
• [ ] User-facing changes are mentioned in CHANGELOG.md.
• [ ] All added/changed functionality is tested.
• [ ] New TODOs link to an issue.
• [ ] Commits meet contribution quality standards.

---

• [ ] This functionality cannot be added in rust-vmm.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (4c8d541) 81.52% compared to head (0c4ec3b) 81.51%. Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4380      +/-   ##
==========================================
- Coverage   81.52%   81.51%   -0.01%     
==========================================
  Files         241      241              
  Lines       29249    29247       -2     
==========================================
- Hits        23844    23842       -2     
  Misses       5405     5405              

Flag	Coverage Δ
4.14-c7g.metal	76.88% <100.00%> (-0.01%)	:arrow_down:
4.14-m5d.metal	78.83% <100.00%> (-0.01%)	:arrow_down:
4.14-m6a.metal	77.94% <100.00%> (-0.01%)	:arrow_down:
4.14-m6g.metal	76.88% <100.00%> (-0.01%)	:arrow_down:
4.14-m6i.metal	78.81% <100.00%> (-0.01%)	:arrow_down:
5.10-c7g.metal	79.79% <100.00%> (-0.01%)	:arrow_down:
5.10-m5d.metal	81.50% <100.00%> (+<0.01%)	:arrow_up:
5.10-m6a.metal	80.70% <100.00%> (-0.01%)	:arrow_down:
5.10-m6g.metal	79.79% <100.00%> (-0.01%)	:arrow_down:
5.10-m6i.metal	81.48% <100.00%> (-0.01%)	:arrow_down:
6.1-c7g.metal	79.79% <100.00%> (-0.01%)	:arrow_down:
6.1-m5d.metal	81.50% <100.00%> (+<0.01%)	:arrow_up:
6.1-m6a.metal	80.70% <100.00%> (-0.01%)	:arrow_down:
6.1-m6g.metal	79.79% <100.00%> (-0.01%)	:arrow_down:
6.1-m6i.metal	81.48% <100.00%> (-0.01%)	:arrow_down:

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[bchalios]

Resolves #4548

[roypat]

Superceded by https://github.com/firecracker-microvm/firecracker/pull/4556